1. Field of the Invention
The present invention relates in general to a method and apparatus for picking up packaged cargo of a flexible sheet material such as paper, film, or nonwoven fabric, and relates in particular to a method and apparatus for picking up a packaged sheet of a desired kind from a number of such packaged sheet of one or more kinds stacked up on a respective one of cells of an automated warehouse, and assorting and stacking the picked packaged sheet on pallets according to destinations, and/or for handling stacked pallets, on which no packaged sheet is stacked, for desired purposes. The description will be hereinafter directed to the handling of paper products although the products to be handled are not limited to them.
2. Related Art
In the pulp and paper industries, a unit of handling of cutting paper is based on "ream". Specifically, one ream is defined by 500 sheets of cutting papers (or 100 sheets of paper boards). In warehouses, the inventories are stored on pallets, each pallet having several tens of reams of the same kind of paper and weighing from about 800 to 1,200 Kg, and measuring about 1.5 to 1.8 m in height.
Clients such as distributors try to keep their inventories as low as possible and thus an order to a paper manufacturer will usually consist of small lots of a variety of paper products. Therefore, the paper manufacturer must ship many different kinds of paper products on a pallet, and in extreme cases, it is necessary to pick up reams of different kinds of packaged products manually one by one.
The warehouses for storing the above-mentioned paper products can be divided into two broad categories: a flat-stacking warehouse and an automated warehouse.
In the flat-stacking warehouse, the paper goods are stored in piles from its innermost part, and to access a ream of one type, it is always necessary that other types of reams piled in front must first be removed by a forklift to make a space before the desired ream can be accessed. Such process is not only time-consuming but is prone to damaging paper goods because of accidental bumping against the stored paper goods during the process of finding and loading the goods.
In an automated warehouse, a storage pallet containing a full load of reams of the desired type of paper goods must first be retrieved out from the rack, and the desired number of reams must be picked out from the storage pallet manually. The remaining goods on the storage pallet must then be reinputted to the original rack. In this type of operation, the stacker cranes are fully busy continually, and in some cases, cause the required shipping schedule to be missed, because some ordered items cannot be accessed in time for shipping. A remedy might be to reduce the number of the shelves or cells facing the stacker crane to less than a third of the existing number, thus considerably raising the effective number of stacker cranes per shelving. The enlarged area for the manual picking operation must also be ensured to handle the increased number of pallets, and the number of men required to handle the goods is increased. Thus, the overall balance, between the benefits gained by automated warehouses and the increased handling costs including the capital investments necessary, largely negates the benefits of automation in such instances.
Commodity papers such as woodfree papers are limited in their selection, and it is rare to receive small lot orders for these types of papers. However, for speciality papers or fancy papers, orders are often received for one ream for each of different colors, basis weights, or patterns. Furthermore, the paper goods such as speciality papers consume far more net storage space than the general purpose papers in an ordinary multi-storied flat-stacking warehouse, because larger access space must be reserved for the forklift for handling the speciality papers.
Furthermore, even in the automated warehouses, economical operation of warehouses becomes difficult when the proportion of speciality papers or the like is high. For relatively small scale operations, twin type stacker cranes are being used, but they are not suitable for large scale operations.